1. Technical Field
This invention relates to a cap for a semiconductor device, which is employed for assembling a semiconductor laser device used in e.g. an optical disk recording/reproducing apparatus, and more particularly to a cap for a semiconductor device in which light-transmissive member is fixed to a cap body using leadless low-melting glass.
2. Related Art
As a semiconductor laser device, the configuration as shown in FIG. 5 is known. This semiconductor laser device includes a disk-shaped metallic stem 1, a semiconductor laser element 2 serving as a light source, and a monitoring element 4 such as a PIN photodiode. The semiconductor laser element 2 is located on the side wall of a metallic block (heat sink) provided upright on the disk-shaped metallic stem 1. The monitoring element 4 is located below the semiconductor laser element 2 for monitoring the output from the semiconductor laser element 2. Lead pins 6 are passed through through-holes 5 which penetrates the metallic stem 1 and glass-sealed therein. The lead pins 6 are electrically connected to the semiconductor laser element 2 and monitoring element 4 through bonding wires 8, respectively. Incidentally, one of the lead pins 6 is welded on the lower surface of the metallic stem 1 as a lead pin for grounding.
The semiconductor laser device is manufactured by hermetically fixing a cap for a semiconductor device 10 (hereinafter also simply referred to as a semiconductor device cap) to an element loading surface of the metallic stem 1 with the semiconductor laser element 2 and other loaded thereon. A cap body 12 is formed in a cap shape to have a light transmissive opening 12a at the end face by press-working a metallic member. And the semiconductor device cap 10 is formed by fixing a light transmissive window 14 of a glass plate so as to seal or cover the light transmissive opening 12a from the inside of the cap body 12. The cap body 12 is fixed to the metallic stem 1 by welding its flange to the edge of the metallic stem 1 (see JP-A-6-5990).
There are several methods of fixing the light transmissive window 14 to the cap body 12. One of them is to heat the cap body 12 in the air to form an oxide film on the surface thereof, fix the light transmissive window 14 through low-melting glass using the oxide film, remove the unnecessary oxide film of the surface of the cap body 12 and thereafter plate the cap body 12 with a corrosion-resistant plating such as a nickel plating, thus completing the product. Another method is to plate the surface of the cap body 12 with nickel, and form an Ni—Pb eutectic alloy layer during fixing owing to an eutectic reaction of a lead component (Pb) contained in the low-melting glass and nickel in the nickel plating at the interface between the low-melting glass and nickel plating so that the light transmissive window 14 is fixed to the cap body 12.
According to the latter method, the plating step after the light transmissive window 14 has been fixed to the cap body 12 is not required. The low-melting glass is not eroded by a plating solution. The step of removing the oxide film is not also required. Thus, this method provides an advantage of simplifying the manufacturing process.
FIG. 4 is an enlarged view of the configuration in which the light transmissive window 14 is fixed to the cap body 12 using the eutectic reaction between nickel and Pb contained in the low-melting glass. At the interface between a nickel plating 18 formed on the surface of the cap body 12 (metal) and low-melting glass 16, an Ni—Pb eutectic alloy layer 20 due to the eutectic reaction between the Pb component contained in the low-melting glass and Ni in the nickel plating is formed.
Meanwhile, in recent years, a method for manufacturing an optical device using the low-melting glass not containing the lead component has been proposed from the viewpoint of environmental protection. For example, there is a method of manufacturing the semiconductor device cap using SnO—P2O5 series glass containing no lead as a fixing glass for fixing the light transmissive window (see JP-A-2003-34549).
As described above, in a process of manufacturing the semiconductor device cap, containment of no lead has been realized by the method using the SnO—P2O5 series glass. However, where the SnO—P2O5 series glass is used as the low-melting glass, as compared with the case of using Pb-series low-melting glass employed in the related art, the SnO—P2O5 series glass is problematic in hermeticiy and endurance. This lead to a problem being incapable of giving sufficient reliability for the semiconductor device cap which requires high hemeticity and endurance.